Burner chamber unit for a thermoelectric generator or the like

ABSTRACT

A THERMOELECTRIC GENERATING ASSEMBLY HAS A COMBUSTION CHAMBER UNIT IN WHICH THE SPACE THROUGH WHICH THE FUEL END PRODUCTS OF COMBUSTION PASS INCLUDES A PLURALITY OF SPACED HEAT-CONDUCTING ELEMENTS EXTENDING TO THE CHAMBER WALL AND DEFINING FLUID COMMUNICATION SPACES THEREBETWEEN, A GAS-PERMEABLE COMBUSTION MEMBER BEING LOCATED IN THE CHAMBER AT LEAST IN PART BETWEEN THOSE ELEMENTS.

Feb- 9, 1971 M. A. RUBINSTElN ET AL 3,561,903

BURNER CHAMBER UNIT FOR A THERMOELECTRIC GENERATOR OR THE LIKE OriginalFiled Sept. 20, 1965 6 Sheets-Sheet 1 IKC. 1,1 IUI l M. A. HUUINBIC-IN:Il ""L- "Uvl'uva BURNER CHAMBER UNIT FOR A THERMOELECTRIC GENERATOR ORTHE LIKE Original Filed Sept. 20, 1965 G Sheets-Sheet 2 Feb. 9,4197

M. A. RUBINSTEIN ET AL BURNER CHAMBER UNIT FOR A THERMOELECTRICGENERATOR OR THE LIKE Original Filed Sept. 20, 1965 6 Sheets-Sheet 5Feb. 9, 1971 M A. RUB|NSTE|N ET AL 3,561,903

BURNER CHAMBER UNIT FOR A THERMOELECTRIC GENERATOR OR TEE LIKE OriginalFiled Sept. 20, 1965 6 Sheets-Sheet 4.

[g H E fl Feb. 9, 1971 M A RUBINSTElN ET AL 3,561,903

BURNER CHAMBER UNIT FOR A THERMOELECTRIC GENERATOR OR THE LIKE OriginalFiled Sept. 20, 1965 6 Sheets-Sheet 5 5f um Feb. 9, 1971 M, A,RUBlNSTElN ET AL 3,561,903

BURNER CHAMBER UNIT FOR A THERMOELECTRIC GENERATOR OR THE LIKE OriginalFiled Sept. 20. 1965 6 Sheets-Sheet 6 Fla? L I ///4 United States PatentO 3,561,903 BURNER CHAMBER UNIT FOR A THERMO- ELECTRIC GENERATOR OR THELIKE Martin A. Rubinstein, Morrisville, Pa., and Charles Teleki, WestOrange, NJ., assignors to General Instrument Corporation, a corporationof Delaware Original application Sept. 20, 1965, Ser. No. 488,483.Divided and this application July 7, 1969, Ser.

Inf. cl. Fzsd 13/00 U.S. Cl. 431-350 Claims ABSTRACT OF THE DISCLOSURE Athermoelectric generating assembly has a combustion chamber unit inwhich the space through which the fuel end products of combustion passincludes a plurality of spaced heat-conducting elements extending to thechamber wall and defining fluid communication spaces therebetween, agas-permeable combustion member being located in the chamber at least inpart between those elements.

This application is a division of our application Ser. No. 488,483,filed Sept. 20, 1965, entitled Thermoelectric Generating Assembly andassigned to the assignee of this application.

The present invention relates to the construction of a thermoelectricgenerator, and in particular to such a construction in which theefficiency of the transformation of energy from fuel to electricity isenhanced and in which the reliability of the apparatus to produce suchenergy Conversion over wide ranges of ambient conditions is greatlyincreased.

The use of thermoelectric electrical generators for providing electricalenergy, particularly in remote locations where normal sources ofelectric power are not available or as emergency power sources for usewhen normal power sources fail, is growing. Two primary limitations onthe use of such equipment are efficiency and reliability.

The more electrical energy that can be produced from a given amount offuel, the less costly is that energy, and the longer can the equipmentbe operated without having to replenish the fuel supply. Thusimprovement in overall efficiency is an obvious need with equipment ofthis type.

The problem of reliability arises to a large extent from the existenceof very large temperature differentials and temperature variations inconnection with the operation of the equipment. Parts must be inintimate connection with one another in order that heat may betransferred therebetween, and such intimate contact must in manyinstances be accomplished over comparatively large surface areas.Nevertheless, the parts in contact are formed of different materialswhich expand at different rates, and hence as temperatures changestresses are produced which, when intense enough or when fluctuated overa sufficiently long period of time, tend to cause physical failure ofmechanical parts.

It is the prime object of the present invention to provide athermoelectric generator assembly construction which solves the abovementioned problems in a manner much more effective than any that havebeen known heretofore, and to do so by means of a construction whichfacilitates assembly and minimizes cost.

In the form here specifically disclosed the generator is designed to usea gaseous fuel such as propane which, when mixed with air in appropriateproportions, will burn without flame and will produce large quantitiesof heat. This burning is accomplished by causing the fuelair mixture topass over tbe surface of a suitable combustion member, generallyprovided in the form of a screen ice through which the fuel-air mixturecan pass. This member may be catalytic relative to the fuel-air mixture,in which case it may be maintained at a temperature below the normalignition temperature of the fuel-air mixture, or it may be of thesurface combustion type, in which case it is maintained at or above thatnormal ignition temperature. In either case the combustion process takesplace on the surface of the member at a temperature much lower than in aflame-type burner. Most of the heat energy liberated by the combustionis transferred from the member to the heat-receiving surfaces of theassembly by infra-red radiation. SomeV of the heat energy liberated actsupon the products of combustion so as to raise their temperature, and aportion of this heat energy is transferred to the heat-receivingsurfaces of the unit as the exhaust products pass over those surfaces.The remainder of the heat energy is lost with the combustion products asthey exhaust from the unit.

In order to facilitate the transfer of heat energy from the combustionarea adjacent the catalytic or surface combustion member to theheat-receiving surfaces of the unit, and provide for increasedefficiency in the operative use of that energy, the combustion chamberis so designed as to maximize the active area of the combustion memberand to ensure that said active area is in proper operative relationshipwith the functionally effective heat receiving surfaces. To that end thecombustion chamber is here taught as being subdivided into a pluralityof sections by means of wall elements which are spaced from one anotherand which are in substantially direct thermal communication with thatwall of the combustion chamber through which heat is adapted to beapplied to the hot sides of the generating elements themselves. Thesewall elements, here disclosed in the form of fins, are located closelyadjacent to the combustion member and, indeed, define a structure aboutwhich the combustion member may be enfolded. As a result both thecombustion member surface area and the heat-receiving surface area aremaximized and are so spatially related as to facilitate efficientinfrared heat transmission.

Moreover, the specific conditions of combustion are controlled in anovel and strikingly simple fashion, thereby to permit variation in theamount of heat which is effectively utilized to produce electricalenergy. This is done by controlling the amount of air which mixes withthe fuel. For a given assembly there is an optimum air inlet rate for agiven fuel flow rate, which will give rise to maximum heat production.If the air flow is permitted to occur at a greater or lesser rate thansaid optimum rate, less of the available heat will be utilized, Aventuri device is used for aspirating the air into the fuel. Byadjusting the size of the passage through which that air flows, eitherbefore it is aspirated into the fuel or after the air and fuel haveburned and are exhausting from the unit, the amount of effective air maybe varied. When the passage size control is located in the exhaustpassage from the combustion chamber the effect of external wind on thepressures within the unit is minimized, and consequently location of therestriction in the exhaust passage is preferred.

In order to take care of the problems presented by the wide ranges oftemperature to which the operative parts are subjected and thedifferential expansion problems produced thereby, the thermoelectricgenerating module, the combustion chamber means engaged with its hotside, and the heat dissipating means engaged with its cold side, are allconnected together in a fashion such as to permit effective andefficient heat transfer while permitting those parts movement relativeto one another to compensate for differences in thermal expansivity.Moreover the thermoelectric generating module itself may incorporate thesame principle of assembly.

In the module itself the thermoelectric elements are mounted Iwithin acasing comprising thin flexible walls which are sealed to one anotherradially beyond the thermoelectric elements, the interior of that casingbeing evacuated. The module also comprises relatively thick, rigid heattransmissive members the outwardly facing surfaces of which arepreferably smooth and flat. Atmospheric pressure, acting through theflexible casing walls upon the evacuated interior of the casing, forcesthe heat transmissive members axially into firm engagement with the hotand cold sides respectively of the generating elements, while permittinglateral movement of the walls relative to the thermoelectric elementswhen temperatures change and the engaged parts expand or contract todifferent degrees. Although the heat transmissive members are rigid,this action is not interfered with and said heat transmissive membersare nevertheless in good heat-transfer relation with said generatingelements via said thin walls. Thus only minimal stresses are exerted onthe thermoelectric elements themselves as temperatures change. As aresult the reliability of these elements, in general the most fragileparts of the entire assembly, is greatly increased. Because the sametype of lateral sliding movement to relieve differentials in thermalexpansion is provided for between the module on the one hand and thecombustion chamber means and the heatdissipating means respectively onthe other hand, temperature-change-induced stress at the interfacesbetween those elements are greatly minimized while effective heattransfer across those interfaces is accomplished. In addition, thedesign also prevents build-up of excessive cornpressive stresses on thethermoelectric elements, by making allowance for the fact that as theunit is brought up to operating temperatures the thicknesses of themodule on the one hand and the dimension of the rigid members of thesupporting structure on the other hand might vary relative to oneanother. The module is held in place by means of a spring reliefmounting which permits variations in appropriate dimensions without anysignificant change in the spring forces.

When air is aspiration-mixed with fuel the amount of air which is thusaspirated will depend in part upon the pressures at the air inlet andexhaust portions of the system. Those pressures may tend to bedifferently affected by ambient conditions such as wind. A gust of windwhich enters the unit will tend to increase the pressure inside the unitat the air inlet, thereby reducing the amount of air which mixes withthe fuel and thus reducing the electric generating efficiency of thedevice.

Means are provided for equalizing the pressure at the inftake andexhaust portions of the fluid ow system, thereby to render the operationof the unit relatively insensitive to wind effects.

To the accomplishment of the above, and to such other objects as mayhereinafter appear, the present invention L relates to the constructionof a thermoelectric generating assembly, as defined in the appendedclaims and as described in this specification, taken together with theaccompanying drawings, in which:

FIG. l is a three-quarter perspective view of a unit comprising twothermoelectric generating assemblies mounted in a typical application,to wit, positioned on a pole together with an associated piece ofequipment for 'which it is to serve as a power supply;

FIG. 2 is a top plan View, partially broken away, of the generator unitof FIG. l;

FIG. 3 is a cross sectional view taken along the line 3 3 of FIG. 2;

FIG. 4 is an end elevational view, partially broken away, of the unit ofFIG. l;

FIG. 5 is a cross sectional view taken along the line 5 5 of FIG. 2;

FIGS. y6 and 7 are cross sectional views taken respectively along thelines 6 6- and 7-7 of FIG. 5

FIG. y8 is a top plan view, partially broken away, of

an alternative embodiment of exhaust means for a plurality of generatorassemblies; and

FIG. 9 is a cross sectional view of an alternative embodiment of thethermoelectric module.

FIG. 1 illustrates a typical application for the thermoelectricgenerators of the present invention, those generators, generallydesignated A, being shown mounted on a pole B which also carries a workdevice C (for example, a microwave relay which is electrically connectedto an antenna, not shown, also mounted on the pole B). The function ofthe generator assembly A is to provide electrical power for the workdevice C, either continuously or whenever a primary source of powershould fail.

The generator A comprises a casing 2 which carries the operative parts,and which is provided with a base housing 4 adapted to be mounted on anysuitable platform 6. The generator A is designed to be used inconjunction Y with a supply of fuel, which may take the form of one Y ormore tanks of a suitable combustible gas such as propane, stored'underpressure. The fuel supply tanks are not shown in the drawings. They areconnected to the generator A by means of pipe 8 which enters the basehousing 4 and is in uid communication with pipe 10 in the casing 2. Inthe form here specifically disclosed, where two separate generatingassemblies are incorporated into the same casing 2, the fuel pipe 8 maybe connected to the individual fuel pipes 10 for each of the twoassemblies via manifold 12.

(In the discussion to follow only a single generator assembly will bedescribed, and it will be understood that the second generator issimilarly constructed and arranged.)

The combustion chamber housing for the generator is generally designated13. It comprises a at end plate 14 to which a cover 16 is secured bymeans of nuts and bolts 17, a gasket 19 being interposed between theparts 14 and 16 at their periphery for sealing purposes. The plate 14 isgenerally flat, and defines that end wall of the combustion chamberhousing through which heat is adapted to be transmitted to thethermoelectric generating elements. The cover 16 extends out from theplate 14 so as to define a space 18 therebetween. The upper wall 20 ofthe cover 16 is provided, at a point remote from the plate 14, with anopening 22 through which the venturi unit 24 extendsJ that unit having aportion 26 extending above the wall 20 and a portion 28 extending intothe space 18 and having a shaped fuel passage 30 formed therein. Anorifice housing 32 is mounted on top of the venturi portion 26, and isthere secured by means of screws 34. It has a depending conical portion36 terminating in a passage 38. A tube 39 of appropriate inner diameteris fitted within the passage 38 and preferably extends up into theinterior of the housing 32, where it may be surrounded by a conical meshscreen 41. The housing portion 36 extends into the passage 40 in theventuri portion 26 and is radially inwardly spaced from the innersurfaces of the passage 40. An opening `42 is provided through theventuri portion 26 into the passage 40, and an air supply tube 44 isconnected thereto, the other end of the air supply tube 44 being exposedto ambient air, as by opening into the base housing 4. The end 46 of thefuel feed line 10 is received inside the housing 32 at its upper end.The mouth 48 of the venturi unit 24 is spaced above the bottom wall 50of tht cover 16.

The use of the tube 39 permits highly accurate sizing of the orificethrough which the fuel flows. The fact that the upper end of the tube 39is above the bottom wall of the housing 32 minimizes the possibilitythat the tube 39 might become clogged by particles entrained in thefuel, and the screen 41 provides additional protection in this regard.

Integrally formed with the wall 14, and extending therefrom into thespace 18, are a plurality of wall elements 52, spaced laterally from oneanother and connected at their upper and lower ends by top and bottomwalls 54. The edges 56 of the walls 54 which extend into the space 18are recessed between the individual wall elements 52, as may best beseen in FIG. 7. A gas-permeable curtain 58 is secured to the edges 56,as by the screws 60 and strips 62 shown in FIG. 5, and extends betweenthe top and bottom walls 54. The curtain 58 defines a combustion member,which may be of the surface combustion type but which is herespecifically disclosed as being formed of a material which will catalyzethe combustion of the fuel employed. The spaces between the wallelements 52 and the walls 54 define the primary combustion spaces orchambers 59.

For combustion-initiation purposes, resistance wire 64 is positioned ontheY venturi-side of' curtain 58, preferably conforming inconfiguration, when viewed in plan, to the curtain 58, the wire 64having its ends mounted on studs 66 which pass through the wall 14 andextend into the space 18. Electrical connections 68 are made to thestuds 66 and hence to the resistance wire 64, those electricalconnections extending through a suitable temperature sensitive switch(not shown) to a source of power (also not shown), which may be astorage battery designed to be maintained in charged condition by theoperation of the thermoelectric generator itself.

The top wall 54 extends closely inside the upper wall of the cover 16,and a gasket 70 may be interposed therebetween for sealing purposes. Thetop wall 20 of the cover 16 carries an upwardly extending tubularportion 72 in which exhaust pipe 74 is received, the top cover wall 20being cut away to define an opening 76 which provides access to theinterior of the pipe 74, the gasket 70 being so shaped as not toobstruct the opening 76. The top wall 54 is provided with a plurality ofapertures 78 which communicate between the primary combustion chambers59, on the one hand, and the opening 76 and the exhaust pipe 74, on theother hand.

The exhaust pipe 74 extends through the top of the casing 2, where it iscovered by a cap 80. The cap 80 is provided with an outer mountingportion 82 received inside aperture 84 formed in the top wall 86 of thecasing 2 and there staked in place. The mounting portion 82 issurmounted by a radially inwardly extending wall 88 from which a tubularportion 90 depends, that tubular portion being snugly received insidethe open upper end of the exhaust pipe 74. A preferably separate partdefined by a bottom wall 92 having an aperture 94 formed therein isreceived in the pipe 74 below the tubular portion 90, the latter servingto retain part 92 in place. The diameter of the aperture 94 is smallerthan the inner diameter of the pipe 74. A cover 96 is provided which maybe secured to the wall 88 and extends radially therebeyond, where it isprovided with depending sides 98, spaces 100 being provided between thecover 96 with its depending walls 98 and the remainder of the cap 80through which exhaust gases can flow. The cover 96 prevents rain fromentering the pipe 74 while permitting exhaust gases to vent therefrom.

The thermoelectric generating unit itself is provided in the form of thediscrete module, generally designated 101, of which two specificembodiments are here disclosed. One embodiment is best shown in FIGS. 4and 5 and the other is shown in FIG. 9. Insofar as the parts of the twoembodiments are essentially the same, they will be designated by thesame reference numerals, reference numerals for the embodiment of FIG. 9being differentiated by being primed.

To describe first the embodiment shown in FIGS. 4 and 5, thefunctionally operative portionally operative portion thereof consists ofan assembly 102 of thermoelectric generating elements appropriatelyarranged so as to have a hot side 104 and a cold side 106. The elements102, here shown only in a generalized fashion because various forms ofspecific construction and arrangement are well known, are receivedwithin a casing formed of a hot side cover 108 and a cold side cover110, both being formed of thin flexible material such as stainless steelsheet. The cold side cover 110 is essentially fiat. The hot side cover108 is provided with a preipheral flange 112 which is sealed to theperipheral portion of the cold side cover 110 in any appropriatefashion, and has a substantially fiat central portion 114 connected tothe peripheral flange 112 by bulged expansion portion 116. The hot andcold sides 104 and 106 of the thermoelectric generating elements 102must be in good thermal connection with the casing covers 108 and 110,but must be electrically insulated therefrom. To that end there isinterposed between the hot side 104 of the generating elements 102 andthe hot side cover 108 a thin intervening two-ply layer 118 which mayconsist of superposed shims of mica and lead, and there is interposedbetween the cold side 106 of the generating elements 102 and the coldside cover 110 a thin intervening two-ply layer 120 which may comprise ashim of mica with a layer of silicone grease loaded with thermallyconductive particles such as aluminum powder superposed thereon. Themica and lead layer 118 and the mica and grease layer 120 play animportant role. The mica plies of these layers provide for electricalinsulation between the thermoelectric generating elements 102 and themodule Walls 108 and 110. The lead and grease portions of the layers 118and 120 respectively provide mechanical compliancy permitting adaptationto the actual surface configuration of the inner surfaces of the modulewalls 108` and 110 and the opposing surfaces of the thermoelectricelements 102. This is of particular importance because of the inner wallof either surface of the module and the opposed surfaces of the elements102 might well depart from an ideal fiat and smooth characteristic.Particularly is this the case where the alternating N- and P-typethermoelectric elements comprising the element assembly 102 havedifferent temperature coefficients of expansion. Moreover, between theopposed surfaces there should be no spaces which are not filled by aheat conductive material; otherwise the thermal contact between the hotand cold walls of the module and the generating elements 102 will beimpared, Both the lead layer and the aluminum-loaded silicon greaselayer will conform under pressure to the exact shape of the inner modulesurfaces and the opposed thermoelectric element surfaces and willtherefore ensure effective heat transmission.

The hot and cold side covers 108 and 110 extend out radially well beyondthe generating elements 102 to the areas where they are sealed. The hotside cover 108 has secured to its outer surface in any appropriatemanner, as by brazing, a comparatively thick rigid plate 122 formed of amaterial such as tellurium copper or stainless steel, which has a verygood heat transmission characteristic. The cold side cover 110 has acomparable thick rigid plate 124 of heat-conductive material secured toits outer surface. Both of the plates 122 and 124 preferably extendlaterally out beyond the thermoelectric generating elements 102, andtheir axially exposed surfaces preferably are made smooth and flat. Theplates 122 and 124 may also be provided with central recesses 126 and128 respectively extending inwardly from their axially exposed surfaces.

Electrical connection to the thermoelectric elements of the assembly 102is made by means of terminals 130 which sealingly extend through thecold side cover 110 and are provided with external terminal portions 132to which leads 134 may be connected. Also extending through the coldside cover 110, and exposed at the circumferential surface of the plate124, is a tube 136 in fluid communication with the space between thecovers 108 and 110. Once those covers have been sealed one to anotherthe generating elements 102 therewithin, there 7 space between thecovers is evacuated via the tube 136, after which the latter is sealedoff.

It is not essential that the plates 122 and 124 be separated from thethermoelectric elements 102 by the walls 114 and 110. Thus, as shown inFIG. 9, the plates 122 and 124 may themselves constitute the upper andlower walls of the module casing, those plates being joined to oneanother by tiexible anges and 112', the latter being provided withbulged expansion portion 116.

The heat dissipating unit, generally designated 137, comprises, as isrelatively conventional, a wall 138 from which a plurality of spacedfins 140 extend outwardly. The wall 138 may be provided with an inwardlyextending stud 142 which is adapted to be received within the aperture128 in the plate 124 on the cold side of the module 101. The end plate14 on the combustion chamber housing 13 may be provided with an enlargedintegrally outwardly protruding portion 144, here shown as somewhatlarger in diameter than the plate 122 on the hot side of the module 106,the portion 144 carrying a projecting stud 146 which is adapted to bereceived in the aperture 126 formed in the plate 122 on the hot side ofthe module 101. The studs 142 and 146 are preferably received somewhatloosely within the respective apertures 128 and 126.

Extending inwardly from the wall 138 of the heat dissipating unit 137are a plurality of rods 148 which pass loosely through openings 140formed in the secured together flanges of the plate 14 and cover 16 ofthe burner B and extend inwardly well beyond those fianges. The ends ofthe rods 148 are threaded at 152, and nuts 154 are received thereon,those nuts forcing washers 156 toward the aperture 150. Compression coilsprings are received on the rods 148 and are compressed between thewashers 156 and the fianged portions of the cover 116 in which theapertures 150 are formed.

FIG. 8 discloses a modification of the exhaust system where a pluralityof individual generating assemblies are provided. In the modificationthe exhaust pipes 74 from a plurality of such generators are each fittedover the inwardly extending ends of tubes 160 which pass through a wall162 of the casing 2 and enter a manifold 164. The tube ends within themanifold 164 are laterally slotted at 166 and are internally threaded at168, and externally threaded plugs 170 are received therein. The extentto which these plugs 170 are screwed into the tubes 160 will determinethe effective size of those portions of the lateral slots 166 throughwhich the exhaust gasses can pass. The manifold 164 may be laterallysurrounded by a casing 172 within which glass Wool 174 or other suitablethermally insulating material is contained. The manifold 164communicates in any appropriate manner with a stack 176 through whichthe exhaust gases can escape to the atmosphere.

An important feature of the design is the provision for minimizingeffects of external air currents, such as winds, on the performance ofthe generator. The motive force imparted to the aspirated combustion airand to the exhausted products of combustion is provided solely by themomentum of the fuel emanating at high velocity from the tube 39,thereby to establish a small negative pressure at the inlet 42 and asmall positive pressure at the outlet 48 of the venturi. Thesepressures, although sufiicient to keep the respective uid streams inmotion under normal conditions when the local pressures at the airintake and gas exhaust regions are the same, are nevertheless small, onthe order of tenths of an inch of water column. If the locally existingpressure at one of these two regions is different from that existing atthe other region by the same order of magnitude as the total pressuredrop established by the venturi, then the flow of intake air will besignificantly affected, thus adversely affecting the performance of theburner. The direct pressure exerted by air currents or winds is 0.2 inchof water column at velocities of around 20 miles per hour and itincreases as the square of the velocity to 1.2 inches of water at 50m.p.h. and 5 inches of water at 100 mph. Thus it is seen that wind canhave a `very detrimental effect on the operation of the burner. This isminimized, in accordance with the present invention, by providing meansto equalize the pressure at the intake and exhaust ends of the air tiowsystem. Thus, as here specifically disclosed (see FIG. 3), the airintake tube 44 opens at its inlet end into an air pressure balancingchamber 45, defined by the base housing 4. The space inside this chamber45 communicates with the external ambient air by means of a number ofrelatively small holes 47 located on the four sides and the bottom ofthe housing 45. The holes 47 on the sides are identical in number andsize; the hole 47 on the bottom may comprise a total area which islarger than that on any of the sides. In addition, a relatively largetube 49 (approximately twice the diameter of the gas exhaust tube 74)vertically traverses the housing 2, one end of the tube 49 opening intothe air balancing chamber 45 and the other end thereof penetrating thetop cover 86 and provided with a cover 80 similar to the cover 80 forthe exhaust tube 74. The tube 49 thus establishes free uid communicationbetween the air pressure balancing chamber 45 and the area at the top ofthe generator, thereby functioning as an air pressure balancing means.The way in which it works is as follows:

(a) If wind impinging on the exterior portions of the generator has onlyhorizontal velocity components, the wind will impinge on one or at mosttwo of the sides thereof. The air forced into the balancing chamber 45by the wind through the openings 47 on these sides will tend to build upthe pressure inside the chamber 45, and hence at the inlet of the airintake tube 44, relative to the pressure existing at the ends of theexhaust tubes 74.

, This will result in a tendency to increase the rate of combustion airfiow into the generator. However, this pressure cannot build upappreciably since it will readily be relieved by air escaping from thebalancing chamber through the holes 47 on the other two sides and thebottom and, mainly, through the large air balancing tube 49. Thepressure increase is very low because, by design, the total areaavailable for air leaving the balancing chamber is much larger than thetotal area where air is forced in by the wind.

(ib) If the wind velocity has a vertical, upward directed component, inaddition to the horizontal components, the situation remains essentiallythe same as in case (a) except that now air also enters through theopening in the bottom; however, it must be realized that upward verticalcomponents of the wind velocity cannot be large, since the generatorsare usually mounted relatively close to the ground and, additionally,any platform or other supporting structure will shield these openingsfrom the wind.

(c) If the wind velocity has a downward directed vertical component, aback pressure will be exerted upon the end of the exhaust tubes 74 whichwould normally tend to reduce the rate of combustion air flow into thegenerator. However, said back pressure is much lower than the directvelocity pressure exerted by the impinging wind due to the specialconfiguration of cover 80. Moreover, that pressure is also exerted onthe upper end of the balancing tube 49 and propagated through it downinto the balancing chamber 4S to the air intake tube 44. Thus, thepressures at the air intake and gas exhaust portions of the system arevery close, if not the same, resulting in only minor changes in thecombustion air flow which will not affect the burner performanceappreciably.

It is desirable to fill the void spaces inside the enclosure by a goodthermally insulating material, preferably fibrous mineral insulation.This reduces extraneous heat losses from the burner housing.

In operation the fuel such as propane gas, coming from a container wherethat fuel is maintained under pressure, ows through the pipes 8 and 10into the housing 46 and through the venturi unit 24 into the space 18.The velocity of the fuel as it escapes from the tube 39` is quite high,

and since the fuel escapes from that spud tip into an enlarged space itwill aspirate air thereinto, the air enter ing via the opening 42 andthe air supply tube 44. The air and the fuel mix in the lower portion ofthe venturi unit and in the space 18 to the left of the curtain 58within the housing 13. This mixing is quite complete, largely because ofthe turbulence involved,

The fuel-air mixture then passes through the curtain 58 into the primarycombustion chambers 59 which are laterally defined by a pair of adjacentwall elements 52, which are closed at their lower end by the lower wall54, which are substantially closed at their upper end by the upper Walls54, and which are closed at their right-hand side, as viewed in FIG. 5,by the wall 14. For starting the burning, when the catalytic curtain 58is initially at low temperature, an electric current is passed throughthe heater wire 64, that wire raising the temperature of the catalyticcurtain sufficiently high so that combustion of the gas will beinitiated. Once combustion has occurred for a short period of time, theentire housing 13 is at a sufficiently high temperature so that theheater wire 64 is no longer needed to bring the curtain up to propertemperature for catalyzed combustion, and when this situation has beenattained the electric circuit to the heater wire 64 is interrupted,preferably by any conventional thermostatic switch.

The curtain 58 constitutes a constitutes a combustion member which,depending upon its composition and the temperatures to which it israised, produces7 initiates or controls combustion of the fuel-airmixture. As here specifically disclosed the member 58 is in the form ofa catalytic curtain, and under those circumstances it need be raisedonly to a temperature which is appreciably below the normal ignitiontemperature of the fuel-air mixture. Should the composition of themember 58 be such as to produce non-catalytic surface combustion, thetemperature of that member would have to be raised to a point equal toor higher than the normal ignition temperature of the fuel-air mixture.In either case combustion occurs, and consequently heat is produced, atand over the surface of the member 58, and the bulk of the heat thusproduced will be transmitted to the inner surfaces of the combustionchambers through radiation, primarily in the infra-red range.

By virtue of the present construction, which provides a plurality ofprimary combustion chambers 59 each defined by projecting walls 52around which the member 58 sinuously extends, the area of active surfaceof the member 58 at which combustion occurs is maximized, and thatsurface is so located relative to the heat-receiving walls of thecombustion chamber that heat transmission by radiation from the surfacesof the member 58 to those walls is effectively and efficientlyaccomplished. Thus, as may best be seen from FIG. 7, the extensivecombustionproducing surfaces of the member 58 are located opposite andclose to the inwardly facing surfaces of the walls 52.

The amount of combustion heat produced, and the proportion thereof whichis effectively utilized, is determined in part by the rate at which fuelenters the system and in part by the amount of air which is mixed with agiven amount of fuel. When the air-fuel mixture is in a predeterminedoptimum proportion the greatest amount of heat is effectively utilized.When the air-fuel ratio differs from that optimum value in eitherdirection, the amount of heat utilized lessens. The air is drawn intomixture with the fuel by aspiration. The present construction providesthat, for a given fuel flow, the amount of air mixed therewith can bebrought to optimum value by providing a restriction of appropriate sizein the flow path of the air. This restriction can be provided either inthe air intake tube 44 or, as here specifically disclosed, in theexhaust pipe 74, that restriction being defined by the opening 94 in thewall 92. Placing the control orifice in the exhaust pipe 74 has theadvantage that wind pressures 10 active at the exhaust pipe cover willnot feed into the combustion chamber as readily when the restriction 94is in place in the exhaust pipe as they would were that restriction notthere located. For each installation a particu lar size for the aperture94 is optimum. In the embodiment of FIG. 8 the effective size of thelateral slots 166 corresponds functionally to the different sizes of theaperture 94 in the embodiment of FIG. 4, and by screwing the plugs 170into or out from the tubes 160 the effective sizes of those lateralslots 165 can be varied, thereby to achieve control of the proportion ofair flow relative to fuel flow.

The manner in which the several units are secured to one another, and inwhich the individual elements of the thermoelectric generating module101 are assembled, accomplishes three results: (l) Assembly of the partsis greatly facilitated; (2) Heat transfer isaccomplished with a highdegree of effectiveness; and (3) Stresses and strains attendant upon thetemperature changes, with accompanying differences in thermal expansionof the individual components, are virtually eliminated.

To consider the thermoelectric module 101 first, the generating elements102 are sandwiched between the plates 122 and 124. Because the module issealed at its edges, because the space inside the module is evacuated,and because the peripheral walls are thin and flexible, atmosphericpressure presses the plates 122 and 124 (with or Without interposed wallparts) firmly against the generating elements 102 and the layers 118,120 interposed therebetween, thereby making for good thermaltransmissive contact and holding the generating elements 102 inposition. The heavy plates 122 and 124 are rigid and flat, and willremain so during exposure to operating temperatures; this is essentialfor providing uniform mechanical pressure forces and thermal contacts,and a uniform thermal flux to the individual thermoelectric elements.The peripheral flanges 112 (or the corresponding parts in the embodimentof FIGS. 4 and 5) are preferably made of low thermal conductivitymaterial to reduce heat shunt losses between the hot and cold sides ofthe module. They are also thin, thereby to provide flexibility to theenclosure to allow for expansion of the thermoelements when brought upto operating temperatures without appreciably changing the magnitude ofthe external pressures exerted upon them. They also provide for hermeticsealing of the module to enable evacuation of the inner cavity thereof.Such differences in thermal expansion as exist between the generatingelements 102 and the plates 122 and 124 or the stainless steel walls 110and 114 result merely in a sliding of the opposed surfaces of thoseelements relative to one another, without the development of anyappreciable stresses or strains, since those surfaces are not positivelysecured to one another. The development of stresses due to dimensionalchanges in the axial direction of the thermoelectric elements and themodule enclosure plates and rigid portions of the module supportstructure is substantially prevented by the flexible peripheral wallportions of the module on one hand, and the loading of springs on theother hand, thereby permitting differential movement of the affectedcomponents rel ative to each other. Since the generating elements 102are the most fragile parts of the assembly, and also the ones wherecracks or breaks would most directly affect the operation of the entireunit, the virtual elimination of stresses in the generating elements 102attendant on temperature change represents a significant increase inreliability and permits the units to be used under a wider range oftemperature change than has formerly been the case.

While the pins 142 and 146 tend to center the module 101 and hold it invertical position relative to the end plate 14 of the combustion chamberhousing 13 and the wall 38 of the heat dissipating unit 137, althoughpreferably with some degree of permitted play, it will be noted that theinterfaces (a) between the hot side plate 122 of the module 101 and theportion 144 of the wall 14 of the combustion chamber housing 13, and (b)between the cold side plate 124 of the module 101 and the wall 138 ofthe heat dissipating unit 134, are both free of positive connection, theparts being urged toward one another, with the module 101 held insandwiched condition, by means of the springs 155. Hence here toodifferences in physical expansion arising from changes in temperaturemerely cause one of the surfaces at a given interface to slide over theother, While the surfaces remain pressed into close heat-transmittingrelationship. Thus throughout the unit, the problems involved indifferential expansion attendant upon changes in temperature are greatlyminimized, if not virtually eliminated.

Moreover, the mounting of the module 101 in nonpermanent fashion, solelyby virtue of the springs 155, greatly facilitates replacement ofindividual modules 101 should that become necessary.

From the above it will be seen that a construction has been disclosedwhich is simple and comparatively inexpensive, which provides forthermoelectric generation in a more efficient manner than has previouslybeen possible, which permits control and adjustment of the combustiontemperature in a novel and effective fashion, which facilitatesreplacement and repair, and which minimizes the need for suchreplacement and repair by substantially eliminating the problems usuallyarising from the differences in physical expansion attendant uponchanges in temperature.

While but a single embodiment of the present invention has been herespecifically disclosed, it will be apparent that many variations may bemade therein, all within the scope of the instant invention as definedin the following claims.

We claim:

1. A burner chamber unit for a thermoelectric generator comprising ahousing with fuel inlet means and exhaust means, a heat-transmittingwall, a plurality of spaced 12 elements extending from said wall towardsaid fuel inlet means, said elements being in essentially directconductive thermal connection with said wall, fluid communication meansbetween the spaces between said elements and said inlet means andexhaust means respectively, and a gas-permeable combustion mmeberinterposed between said inlet means and exhaust means and located atleast in part between said elements.

2. The chamber unit of claim 1, in which said member is mounted on saidelements and extends sinuously between the ends of adjacent elements.

3. In the chamber unit of claim 2, a wall joining said elements at theirupper ends and defining a top wall for the spaces between said elements,said fluid communication means comprising apertures through said topwall between said elements. Y

4. In the chamber unit of claim 1, a top wall joining said elements attheir upper ends and defining a top wall for the spaces between saidelements, said fluid communication means comprising apertures throughsaid top wall between said elements.

5. In the chamber unit of claim 4, in which said top wall is recessedbetween said elements in a direction toward but short of saidheat-transmitting Wall, said member being mounted on said elements andessentially conforming in configuration to the recessed edge of said topwall.

References Cited UNITED STATES PATENTS 2,601,299 6/1952 Kennedy 43l-328X 3.215.561 11/1965 Rosenfeld 136h200X 3,225,757 12/1965 Keller126-91 EDWARD G. FAVORS, Primary Examiner U.S. C1.X.R.

